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June 2007 4x4 Tech Questions - Nuts & Bolts

Posted in How To on June 1, 2007
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Confused? E-mail your questions about trucks, 4x4's, and off-roading tech using "Nuts, I'm confused" as the subject and include a picture (if it's applicable). Digital photos must measure no less than 1600 x 1200 pixels (or two megapixels) and be saved as a TIFF, an EPS, or a maximum-quality JPEG file. Also, I'll be checking the forums on our Web site (, and if I see a question that I think more of you might want to have answered, I'll print that as well. Otherwise drop it old-school style with the envelope addressed to the address below. Letters published in this magazine reflect the opinions of the writers, and we reserve the right to edit letters for clarity, brevity, or other purposes.

Write to:
Nuts & Bolts
4-Wheel & Off-Road
6420 Wilshire Blvd.
Los Angeles, CA 90048-5515
fax 323.782.2704

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Question: I have a '47 Ford truck with 12 inches of homemade suspension and Bronco axles. I have figured out the final gear ratio of the dual T-case setup I want to run (203-205) to be 145:1 using my NP435 and 5.43 gears in the axles. I would like to run 39.5s and was wondering what this would make my final gear ratio. Would this tire and gear setup allow me to do 70 mph without blowing my engine, a fuel-injected 302?

Answer: As you seem to know, the final gear ratio is different in every gear. Your crawl ratio is determined by multiplying your lowest low-range transfer case ratio by your lowest transmission ratio by your ring-and-pinion ratio. Your cruising ratio is determined by multiplying your high-range transfer case ratio by your transmission high-range ratio by your axle ratio. Though the tires affect your final drive, they are not considered part of you gear ratio. In your case I feel 5.43 is just a bit too low for 39.5-inch-tall tires when you are cruising, but it will be great if you are rockcrawling.

Remember your NP435 transmission has no overdrive, only a 1:1 high gear, and thus at 70 mph your V-8 engine will be running at just over 3,200 rpm. Here is the equation:

RPM = MPH x Axle Ratio x High Range x Top Gear x 336
Tire Diameter (in)

Now with your numbers:

3,233 = 70 x 5.43 x 1 x 1 x 336

The issue is that I do not know your vehicle's powerband, most economical rpm, or redline for your engine and truck to help determine what gear ratio would work best. The powerband is usually defined as the most efficient engine speeds. These speeds often range from the max torque rpm to the max horsepower rpm but also covers all rpm that result in 75 percent or more of max torque. The most economical rpm is the point where your engine, truck, and load get the best fuel economy while moving the maximum amount of miles. This depends on everything from aerodynamics to engine build. The redline of your engine is the rpm at which parts like pistons, valves, and bearings get upset due to lack of balance, and the excessive speed causes the engine to start to self-destruct.

So what does this all mean for you? Though I think 3,200 rpm sounds a bit high for a Ford 302 V-8 to be spinning while cruising at 70 mph, I doubt it will blow up. It's probably a fair bit under redline rpm. Plus, back in the '80s Ford trucks were available with the 302 V-8, and they could also be had with 4.10 gears, a nonoverdrive transmission, and 29-inch-tall tires from the factory. If all these options were chosen the truck would be spinning 3,300 rpm at 70 mph-though other gear options had 70 mph seeing 2,500 or 2,800 rpm, which sounds more pleasant to me.

To get back to factory specs simply do the following equation with 2,500 or 2,800 as your rpm:

Final Drive Ratio = RPM x Tire
MPH x 336

Then just try to shoot for that. However, you could do some trick machine work and such to allow your engine to rev at high rpm, and then 5.43s are probably not a problem. The best thing you can do is talk to your engine builder to determine where the powerband is and where it should be when cruising for economy.

This is a great question and qualifies for Tech Question of the Month. Since you'll be doing some gearwork I'm sending you a copy of the new book Differentials: Identification, Restoration, and Repair by Jim Allen and Randy Lyman. Allen is a longtime tech writer who specializes in 4x4s, and Lyman is the namesake of Randy's Ring & Pinion, the largest aftermarket supplier of ring-and-pinions in the U.S. The 380-page book covers more differential tech and info than the average human could ever wish to know, but truck guys like us can't get enough of it. Whether you want step-by-step instructions for setting up gears or identifying your favorite truck axle parts, this book is awesome. All our other readers can order a copy from Randy's Ring & Pinion, 800.209.2881,

Question: I am the proud owner of a '76 Jeep CJ-7. It has 38-inch Boggers, a spring-over conversion, Dana 60s front and rear, a 383 stroker, an Atlas transfer case, and 4.56 gears. I want to install a set of Truck Nutz on the back of my rig and don't know where to begin. Could a weekend wrencher handle the install or should I hire a professional? Will they hurt my departure angle? What color is the most durable? With so many different manufacturers, how do I know who has the best nutz overall? Finally, how do I keep my nutz clean? I hope you can help me. I look forward to your response.

Answer: You don't know how often I get asked this question, and to tell you the truth it's a very valuable and insightful query you have posed. Truck nuts, tailgate testes, bumper balls, chassis cajones, differential danglers...the market is booming these days, but unfortunately we just don't have the proper facilities to test the best make and model for your ride. I am, however, sure that with a name like Mongoose you have more than your fair share of ladyfriends hanging about, and they could most assuredly help you pick out just the right sack of jewels for your Jeep.

Oh, and another thing. When it comes time to tighten up your nuts and keep them clean, don't be afraid to ask those members of the fairer sex to help you out as well. However, I have heard that sometimes womenfolk can be real ballbusters, so take that into consideration-especially if she shows up with hammer and a vise. Finally, yes, they will impair departure angle, but only on warm days when they hang low. On colder day I wouldn't doubt they'd shrink up out of the way.

Question: Ihave a '99 Dodge Ram 1500 5.9L with a 46RE auto trans and a noisy 150,000-mile wornout NP231 transfer case. Can I replace my transfer case with an NP241V (Rocktrac)? I already have the Rocktrac case, so what issues would I have to look forward to when installing it? New drivelines? Shift linkages? Or would it be cheaper and easier to get a direct replacement and just install it?

Answer: First be sure you have a true Rocktrac transfer case. A Rocktrac should read "241J" and "400" in the Ratio blank. I asked around, and no one has heard of a 241V. Assuming it is a Rocktrac, it should bolt up, but the input gear length could be an issue. The Ram's 231 uses a standard-length 23-spline input, and the Rocktrac uses a short 23-spline input. Spline and seal engagement may be an issue. The front driveshaft should be close and might be able to be reused, though measuring would be advised. Your factory rear driveshaft uses a slip yoke where the Rocktrac has a fixed rear yoke, so a new rear shaft will be needed. The linkage should be fine or darn close. It will probably be cheaper to use another 231, but I agree the swap would be better with lower low-range and the fixed rear output.

Question: All the time I see radiators in the rear of a vehicle. Twice now a friend and I have put the radiators in the back with no luck! I even used mandrel-bent tubing for better flow. The engine stays cool till you shut it off, then it blows half the coolant out the overflow and boils the engine. We used a 15-pound radiator cap hoping to bring the boiling point up. Is the only solution an electric water pump to run after it is shut off? Both trucks are street-driven, and I was told not to use them on the street.

Answer: Putting the radiator in the back of your truck isn't a bad idea, but it does involve some considerations. One important item is that even though the radiator would be in the back of your truck, it still needs sufficient airflow. Putting it right up against the cab isn't the best idea. It needs enough space around it to let air flow in and out of the core.

I've discussed your issue with the folks at Ron Davis Radiator (623.877.5000), and you need to have a few things. First and foremost is a quality overflow catch can. Nearly every engine-especially an iron block engine-continues to produce heat after you shut it off, and it will burp coolant out as it heats up for a while. If you can build a big enough catch can, you can catch the coolant so it can be pulled back into the radiator as the engine cools.

Second, it is important to get the coolant filler neck above the engine to get all the air out of the system. This will also help cool the engine better.

It is also important to use a good electric fan or two. Ron Davis uses and recommends Spal fans. A good tight fan shroud is important, especially if you do not have direct airflow. These fans should be run off of a thermostatic control so they can keep running for a bit after the engine is shut off. Also, if you are running hard in the sand or mud, let the engine idle for a minute before shutting it off to help bring the temp down. As a worst-case scenario, you could plumb and wire an electric pump bypass that would kick on with the electric fans after you shut the engine down, but I would stick with the mechanical pump for the street.

Question: I have an '83 CJ-7. I have swapped in a GM 350 and a Turbo 400 tranny. I want to swap in a set of 3/4-ton Chevrolet axles, but I'm concerned about the caster camber angles on the front axle. I would like to know what I would need to fix these angles.

Answer: This is a great followup to last month's Tech Question of the Month about putting full-width axles under a Jeep YJ. GM 3/4- and 1-ton front axles have the passenger-side spring perch machined into the cast part of the axlehousing. Because of this, the pinion angle and caster angle are set towards each other from the factory, between 2 1/2 and 7 1/2 degrees up for pinion and about 6 degrees back for caster.

As for camber, it can be slightly adjusted at an alignment shop with shims if needed but isn't as detrimental and most likely is set from the factory.

When going to the GM axles under your Jeep, you'll need a full-width kit like the versions we mentioned last month from either Blue Torch Fabworks (334.673.2755, or Poison Spyder Customs (303.777.4820, By simply going spring-over you will gain a fair bit of lift, and if you go up to a 2-inch lift spring I am told you can often squeeze a 40-inch-tall tire under a Jeep with some body trimming or a high clearance hood like those sold by 4-Wheelers Supply (602.273.7195, Also it seems that with a 2-inch lift spring or less you can usually make the factory pinion angle work and not have terrible caster as long as the mounting points are similar to those on a GM truck. Most of my trucks have about 3-6 degrees of caster.

If you go to a taller lift you'll need to crank up the pinion angle, and this would reduce your caster, at which point you need to look into getting your axletubes pressed out and reset for your desired caster and pinion angle. Some folks use front axle shims that can compensate for misaligned pinion angle and caster. Bolted to the front leaf spring with the center pin, they are usually OK, but I am not a huge fan of front axle shims and especially not front lift blocks because of the possibility that they can come out during hard braking.

Question: I have a '70 350 Chevy with a Comp cam, AFR aluminum heads, and an Edelbrock fuel-injection system. I wanted to put it in a YJ Jeep but can't find anything on emissions and how to install it in a newer Jeep from an emissions perspective. Do you have any information? Thank you.

Answer: I have looked into the engine swap laws in California, and though laws vary across the nation it seems that the rule of thumb is the engine must come from a vehicle that is the same year or newer than the vehicle it is going into, and it should have with it the factory-installed emissions systems. Also, the engine must come from the same class of vehicle as it is going into, such that a passenger car cannot get an engine from an industrial truck, though most pickup engines from up to 1-tons can be swapped into smaller vehicles like Jeeps. Since you say you want to put this V-8 into a Jeep YJ and they were only made from 1987 to 1996 and the engine is a '70, this swap is probably not legal. Your state may be different, but you need to check with your local emissions or inspection laws first. Some regions of the country don't have emissions testing, but that doesn't mean you can legally stuff whatever you want under the hood; it just means you may be a little harder for the authorities to catch.

Question: I own an '83 Dodge with a Dana 60 front and a Dana 70 rear axle. I have recently purchased a set of 395/85R20 Michelin XMLs (46 inches tall). I had not anticipated that these tires would be significantly heavier than a typical set of 44s. I now have concerns that the axles will not hold up to the added mass, particularly the front Dana 60.

I am now weighing my options. While Rockwells are cool and Dynatrac now offers a massive front Dana 80, I cannot afford the large lump sum of cash I'll need to purchase them. I'd like to keep the axles I already have and build them up. At least I know they fit the truck, and I own them. Some years ago, there was a four-part article "Ultimate Super Duty" in your magazine [beginning Aug. '02]. The truck in this article had a Dynatrac ProRock 60 front axle and the same size and brand of tires I plan to use. According to the article, the truck did bust a 35-spline stub shaft, which was attributed to a steering failure. Did that Dana 60 really hold up well? Or was the truck prone to more axle-/stub shaft failures after the story ended?
Ed R.

Answer: 4-Wheel & Off-Road magazine still owns the Ultimate Super Duty but we rarely run the 46-inch Michelins on it even though they made the truck look awesome. After it broke a steering box and a stub shaft on the 2002 Ultimate Adventure, it was followed with two more broken front axleshafts. In the rear we broke one axleshaft, the ARB locker, and spun a tube in the Sterling housing. Nowadays there are chromoly shafts available from CTM racing (760.450.0006), Superior Axle and Gear (888.522.2953), Alloy USA (866.35.ALLOY), and Yukon ( Also, there are 300M U-joints from CTM available which are extremely strong compared to the factory parts we had in the Ultimate Super Duty. Dealing with the broken housing could be done with a substantial bridge/gusset if you can weld. However, you are then moving the weak point elsewhere such as to the ring-and-pinion, and the front low-pinion 60 will be the first failure I'd expect. I know you are on a budget and I understand that the Michelins can be had cheap from military surplus yards and Internet auction sites, but I would advise against using them in extreme terrain with anything less than Dynatrac's Pro-Series Dana 80, Rockwell 2 1/2-ton axles, or some of the larger Mercedes Unimog portal axles, like the U-1300 variant. I see three real options: more axle, less tire, or gentle driving. In the tire category you could also consider grooving the tires to remove weight. In fact I have seen these Michelins grooved not only on the tread but also on the sidewall, though I'm sure they were never designed for sidewall trimming. You could go with the lighter, yet probably more expensive, 46-inch Mickey Thompson Baja Claws (330.928.9092), or 44-, 47-, 49-, or 53-inch tires from Interco (, but I fear unless you get down to 44s you'll still be breaking stuff in your 1-tons. If your axles are unlocked, they might live a while longer, but performance will be greatly hindered. I hate to say it, but I think you should go bigger for axles or smaller for tires, neither option being cheap.

Question: I have a '71 Chevy 3/4-ton 4x4 pickup (350-350 205 NP). The truck has a lot of miles and the history of the running gear is unknown, but it seems solid. The problem is that the gear lube from the transfer case is being pushed through the speedometer cable and leaking on the driver-side floorboard. I have checked and cleaned the transfer case vent several times. I have blown through the vent, and it is free. I also removed the steel cap from the vent and attached a rubber hose and routed it up to the firewall, but still no help. The lube in the transfer case is a good-quality 80/90 with 1 quart of Lucas additive. Could the transfer case be building up too much pressure for the vent to work correctly? If so, how do I fix it? Please help before my wife kicks my ass for tracking gear lube in the house.

Answer: I spoke to the guys at Performance Automotive and Transmission Center (888.877.1008), and they said that the plastic speedometer gear can either get a small groove worn into it or the small lip seal can start to leak around it, and the next thing you know there's some gear lube in your speedometer cable. Then it's like a small-grain auger or drill bit just grinding around and pumping the lube up into your cab and out onto your foot. PATC can supply the parts to repair the leak, but be sure to clean or replace your speedo cable as well.

Another thing to check, if you have an aftermarket manual oil pressure gauge that actually uses a long plastic tube running from the engine, is that it hasn't sprung a leak. You may be getting oil behind the dash as well, and it could be dripping down onto your floor. Make sure the oil is gear oil or engine oil to verify.

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